Typical technology for antilock braking are based on the two following principles: (1) the brake is controlled in a cyclic sequence consisting of periods of pressure application, pressure dump, and pressure hold according largely to the comparison of wheel deceleration with prescribed thresholds, and, to a lesser degree, the wheel slip information, and (2) such pressure cycles control the average wheel slip to maximize the road adhesion for maximum tire tractive force in the longitudinal direction. This type of control is generally known as peak-seeking control.
The peak-seeking method offers the best performance in terms of the shortest stopping distance during braking when vehicle motion is restricted to a straight-line maneuver. Under this situation, the only tractive force the tire needs is in the longitudinal direction. Two characteristics of that method is, first, since the control results in hunting around the maximum longitudinal tractive force, the average longitudinal tractive force is lower than the available maximum force, and second, it cannot provide additional lateral tractive force for cornering during antilock braking.
An algorithm has already been proposed in "Brake Control for Wheel Slip Regulation", No. 29549, Research Disclosure, November 1988, for regulating the wheel slip at a different level than that corresponding to the maximum longitudinal tire tractive force when the need of vehicle cornering is called for during antilock braking. The advantage of controlling the wheel slip at the different level is to gain additional lateral force for cornering as desired. That system computes the wheel slip based on wheel speed and vehicle speed, wheel-slip error, the rate of wheel-slip error and a linear combination of wheel-slip error and the rate of wheel-slip error as a control index; and determining the desired status of the electrohydraulic brake actuator. The effect of cornering and of vehicle steering geometry on the wheel-slip at each wheel is not considered, rather a single wheel slip for all wheels is determined.